The invention relates to a gas and fluid sealing connection between a plastic body and a metallic body which is embedded into the plastic body by means of flowing the plastic synthetic material mass under pressure in a form. The invention relates also to the method of forming such a connection.
The gas and fluid sealing connection of metallic bodies, for example, pipes or threaded inserts, with a plastic body by means of extrusion coating of the metallic body by the plastic material under pressure or by flowing the plastic material around the metallic body in a form involves large difficulties. Especially with changing temperatures, because of the different thermal coefficients of elongation between the plastic and the metallic material, gaps or slots are formed through which the gas or fluid medium can flow from one side of the completed plastic body to the other side. Also, the known arrangements, involving the formation of grooves in the outer surface of the metallic body or the use of metallic bodies with wavy, rippled or knurled outer surfaces to improve the gas fluid sealing of the connection between the plastic and the metal, are unreliable over a long period of time.
It is already known from DE-AS (German Examined Published Application) 10 01 483 to provide the outer skin or surface of the metal part to be embedded with sintering or injection of a highly porous metal surface. The sealing connection between the thus prepared metal part and a plastic part is accomplished with a connection layer, such as soldering, between the plastic material and the porous metal surface. This particular process demands several additional manufacturing stages and therefore is also correspondingly expensive.
Furthermore, it is also known from DE-PS (German Patent) 28 19 017 to insert a pipe in the plastic, the wall strength of which pipe is so selected that it is physically deformed under the plastic injection pressure. Such a process is usable for only a small range of constructions because of the required thin wall strength of the metal part to be embedded.
The invention is based on the problems of providing a gas fluid sealing connection between a plastic body and a metallic body to be embedded therein by flowing around of the plastic material under pressure. The invention is further based on the problem of providing a process for manufacturing a gas and fluid sealing embedding of a metallic body in a synthetic material body, which process is simple and useable for a wide range of applications and which avoids the occurance of sealing losses.
These problems are solved, according to preferred embodiments of the invention, by providing the metallic part to be embedded with a groove on its outer surface and placing an elastomeric sealing ring in the groove prior to applying the plastic material under pressure. In certain preferred embodiments, the elastomeric sealing ring is dimensioned to fill the axial (direction of the tube or other metallic insert to be embedded) extent of the groove in the metallic part while being spaced from the bottom of the groove, the groove bottom serving as an expansion volume space which accommodates inward movement of the sealing ring during the application of the plastic. In other preferred embodiments the sealing ring fills the groove in the metallic part but is formed of closed pore elastomeric foam so as to form to own expansion volume to accomodate the application of the plastic under pressure.
At the connections, according to the invention, a circumferential groove is provided in the region of the metallic body to be embedded, which groove carries the ring of elastomeric material and which elastomeric ring fills the groove in the axial direction, whereby the groove is so shaped that it possesses an expansion volume in the region of the bottom of the groove which is not filled by the elastomeric ring. During the embedding process, when the metal body is subjected to synthetic material plastic mass under pressure, the ring can expand into this expansion volume and, after the hardening of the plastic material, develops the necessary return resilience to assure the sealing connection. In the event that a ring made out of closed pore elastomeric foam is used, the expansion volume is not needed.
The manufacture of such a sealing connection proceeds as follows: The metal body to be embedded is provided in a normal manner in the area where it is to be connected with the plastic material with one or several circumferential grooves. In at least one of these grooves there is placed an elastic sealing ring which fills that groove in the axial direction and is formed of temperature resistant elastomeric material. It is important to assure that the groove accomodating the sealing ring is so shaped that it possesses an expansion volume which is not filled by the elastic ring in the region at the bottom of the groove. The metallic body, together with the sealing ring, is then placed in the necessary apparatus for the manufacture of the plastic part, which apparatus (for example, an injection molding form) is closed and the metallic body is then embedded under pressure in the plastic material disposed in the form of injected into the form. The pressure in the form of mold compresses the elastic sealing ring in such a manner that upon the hardening of the casting material an excellent sealing strength results with a return resilience pressure of the sealing material. In order to facilitate this spring back resiliance, the groove must be so shaped that it possesses an expansion volume in the region of the bottom of the groove which is not filled by the ring so that a compression of the sealing ring is facilitated. In order to assure that the plastic material does not flow into the expansion volume space during the embedding process, the sealing ring must fill the groove in the axial direction and thereby protect the expansion volume against the entry of the plastic material. It is especially advantageous if the groove is formed as a wedge groove wider at the outside surface. It is contemplated by the invention to have embodiments with several grooves and associated sealing rings embedded in same. The sealing effect is thereby increased, however it is in such case necessary that the plastic material body exhibit a large wall strength in order to accommodate these additional seals.
Embodiments of the invention are also contemplated with the expansion volume in the region of the bottom of the groove dispensed with and instead a sealing ring is used which is formed out of closed pore elastomeric foam. In this case the "expansion volume" occurs inside the sealing ring itself because the pores of the foam serve as the expansion accomodating volume.
Preferred plastic body material to be used with the invention include plastic synthetic material, for example polyolefin, polyvinylchloride, polystyrol, polymethylmetacrylate, polyacetate, polycarbonate, polyathylenterephtalate, polyamide, as well as duroplastic synthetic material, for example phenolformaldehyde-pressing mass, polyetherresin, epoxideresin, melamineresin, or plastic or heat platified unfinished plastic (extrusion). It is important that the metallic body is surrounded in the form or mold by the plastic mass under pressure, whereby the sealing ring develops a return resilience after the hardening of the plastic mass.
As material for the sealing ring, the normal elastomeric materials should be used. Primary materials for the sealing ring include the natural butyl-, nitril-, chlorprene- rubbers, acrylic and silicone fluid, thiokol rubber and fluoro-elastomers. The selection of these sealing materials should be made with a view to the temperature at which the embeddment of the plastic body takes place as well as with a view to the characteristics of the material which will be sealed against during use of the sealing connection.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.